NTC (negative temperature coefficient) thermistors are semiconductor ceramics whose resistance decreases with increasing temperature, making them essential components in various temperature sensing applications. Typically, ceramic materials are sintered at high temperatures exceeding 1,150°C. However, in laminated devices incorporating internal electrodes, co-sintering can lead to cracking and mechanical failure due to mismatches in the thermal expansion coefficients between the ceramic layers and metal-based electrodes. Moreover, the use of noble metal electrodes increases production costs. To address these challenges, a low-temperature sintering approach is required. Previous studies have demonstrated that incorporating glass frit can reduce the sintering temperature of ceramics, although this often results in increased electrical resistance. In this study, NiMnCoO₄ (NMC) ceramics, as a representative NTC thermistor composition, were prepared with the addition of 10 wt% glass frit. To mitigate the resulting increase in resistivity, trace amounts (1 wt%) of various metal oxides, including CuO, ZnO, and MnO, were introduced. Among these, the addition of CuO notably decreased both the resistivity and B constant values. In contrast, MnO had little effect on resistivity, while ZnO led to an increase. With respect to the B25/85 constant, samples containing MnO and ZnO exhibited higher values than those without metal oxide additives. These findings indicate that the incorporation of 1 wt% CuO is effective in reducing the increased resistivity in NMC ceramics subjected to low-temperature sintering via glass frit addition.
NTC thermistors are essential components widely used for temperature sensing in various electronic sensor applications. However, conventional NTC thermistor ceramics typically require high sintering temperatures above 1150℃, necessitating the use of high-cost noble metal electrodes such as palladium (Pd) or platinum (Pt), which increases the overall manufacturing cost. In this study, low-melting-point oxides were successfully introduced as sintering aids to reduce the sintering temperature of NiMnCoO₄-based semiconducting ceramics. As the additive content increased, the B constant and average grain size exhibited an increasing trend, while the sample containing 5 wt% additives showed the lowest room-temperature resistivity. Furthermore, samples sintered at 1000℃ demonstrated slightly higher room-temperature resistivity and B constant values compared to those sintered at 1150℃. These results confirm that the addition of low-melting-point oxides is effective in lowering the sintering temperature of NiMnCoO₄ ceramics, suggesting the potential for reducing production costs and improving design flexibility in thermistor fabrication.
Red phosphor in glasses (PiGs) for automotive light-emitting diode (LED) applications were fabricated with 620-nm CaAlSiN3:Eu2+ phosphor and Pb-free silicate glass. PiGs were synthesized and mounted on high-power blue LED to make a monochromatic red LED. PiGs were simple mixtures of red phosphor and transparent glass powder. After being fabricated with uniaxial press and CIP at 300 MPa for 20 min, the green bodies were thermally treated at 550℃ for 30 min to produce high dense PiGs. As the phosphor content increased, the density of the sintered body decreased and PiGs containing 30% phosphor had a full sintered density. Changes in photoluminescence spectra and color coordination were studied by varying the thickness of plates that were mounted after optical polishing. As a result of the optical spectrum and color coordinates, PiG plate with 210 μm thickness showed a color purity of 99.7%. In order to evaluate the thermal stability, the thermal quenching characteristics were measured at temperatures of 30~150℃. The results showed that the red PIG plates were 30% more thermally stable compared to the AlGaInP red chip.
Convectional PZT based piezoelectric ceramics have to sinter at high temperature about 1,200℃ for their suitable electrical properties. However, some issues: low temperature sintering piezoelectric ceramic composition and reliable internal electrode, have recently attracted a great deal of interest as a highly efficient multi-layered piezoelectric ceramics. In order to optimize low temperature sintering conditions of thick-film PMN-PZ-PT ceramic, it was investigated sintering and piezoelectric properties according to the change of LiBiO2contents. Thus, the superior piezoelectric properties were found at the pallet type PMN-PZ-PT optimized with low sintering processing at 925℃ including 7 wt% LiBiO2sintering aid. Consequentially, we successfully manufactured thick-film PMN-PZ-PT ceramics, which had superior piezoelectric and dielectric properties, with 5 wt% of LiBiO2sintering aid at temperature of 900℃.
In this work, [Pb(Mg1/2W1/2)0.03(Ni1/3Nb2/3)x(Zr0.5Ti0.5)0.97-xO3-BiFeO3] (x=0.02 to 0.12) composition ceramics were fabricated by the conventional soild state reaction method and their microstructure and piezoelectric properties were investigated according to PNN substitution. The addition of small amount of BiFeO3, Li2CO3, and CaCO3 were used in order to decrease the sintering temperature of the ceramics. The XRD (x-ray diffraction patterns) of all ceramics exhibited a perovskite structure. The sinterability of PMW-PNN-PZT-BF ceramics was remarkably improved using liquid phase sintering of CaCO3, Li2CO3. However, it was identified from of the X-ray diffraction patterns that the secondary phase formed in grain boundaries decreased the piezoelectric properties. According to the substitution of PNN, the crystal structure of ceramics is transformed gradually from a tetragonal to rhombohedral phase. The x=0.10 mol PNN-substituted PMW-PNN-PZT-BF ceramics sintered at 920 showed the optimum values of piezoelectric constant(d33), piezoelectric figure of merit(d33·g33), planar piezoelectric coupling coefficient(kp) and density : d33=566 [pC/N], g33=29.28 [10-3mV/N], d33·g33=16.57 [pm2/N], kp=0.61, density=7.82 [g/cm3], suitable forduplex ultrasonic sensor application.
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Fabrication and performance of PNN-PZT piezoelectric ceramics obtained by low-temperature sintering Jing Zhang, Yuansong Zhang, Zhoumin Yan, Anjiu Wang, Ping Jiang, Min Zhong Science and Engineering of Composite Materials.2020; 27(1): 359. CrossRef
In this study, (1-x)Pb(Mg1/2W1/2)0.03(Ni1/3Nb2/3)0.09(Zr0.5Ti0.5)0.88O3 + xCeMnO3 (x= 0∼0.02) ceramics were prepared by Columbite precursor method. The phase structure, ferroelectric and piezoelectric properties were systematically investigated. It was found that PMW-PNN-PZT possessed superior electrical properties due to its composition close to the MPB (morphotropic phase boundary). Coercive electric field of 10.05 [kV/cm] and density of 7.88 [g/cm3] were obtained when the substitution amount of CeMnO3 is x=0.02. In contrast, specimens with x=0.01 showed the mechanical quality factor(Qm) of 1,091 and the electromechanical coupling factor(kp) of 0.613.
We investigated the effect of excess CuO on the sintering behavior, ferroelectric, andpiezoelectric properties of lead-free Bi0.5(Na0.82K0.18)0.5TiO3 (BNKT) ceramics. The addition of excess CuOwas found to greatly contribute to the densification and grain growth, however, excess CuO over 3 mol%was precipitated at grain boundaries after sintering. BNKT with 1∼2 mol% CuO in excess sintered at975℃ showed piezoelectric properties comparable to those of unmodified BNKT sintered at 1,175℃. These results seem meaningful for its application to low cost multilayer actuators (MLAs) becauselow firing ceramics make it possible to apply less expensive base metals to the inner electrode ofMLAs.
Vibration Characteristics of Stacked Piezoelectric Transducers Dae Jong Kim, Jin Oh Kim Transactions of the Korean Society for Noise and Vibration Engineering.2015; 25(3): 199. CrossRef
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